1. Field of the Invention
The present invention is directed to an electrodynamically operated shockwave generator of the type having a shockwave source with an electrically conductive membrane an electrically driven coil, with shockwaves being generated in an acoustic propagation medium adjacent the membrane by rapid repulsion of the membrane from the coil when the coil is supplied with a high-energy pulse. The invention is more specifically directed to such a shockwave generator wherein one of the electrically conductive components of the shockwave source contains material which can be placed in a superconducting condition, and the shockwave generator includes means for placing the material in the superconducting condition.
2. Description of the Prior Art
Electrodynamic shockwave generators are known in the art which can be used for a variety of purposes, for example, in medicine for non-invasive fragmenting of calculi situated in the body of a patient, or for non-invasive treatment of pathological tissue conditions in a patient. Such shockwave generators can also be utilized for materials inspection, when such inspection requires charging the material with shockwaves. The shockwave generator is always acoustically coupled in a suitable manner to the subject which is to be acoustically irradiated, so that the shockwaves generated in the acoustic propagation medium, which is a part of the shockwave generator, can be transmitted into the subject. The shockwave generator and the subject to be acoustically irradiated must be aligned so that the region of the subject which is intended to be acoustically irradiated is situated in the propagation path of the shockwaves. If the shockwave generator generates focused shockwaves, it must also be assured that the region of the subject to be acoustically irradiated is situated in the focal region of the shockwaves.
A shockwave generator of this type is described in U.S. Pat. No. 4,674,505. This shockwave generator is a so-called electrodynamic or electromagnetic shockwave generator. In such a shockwave generator, the coil creates a magnetic field extremely rapidly by being charged with a high-voltage pulse. The magnetic field induces a current in the adjacent membrane which is opposite in direction to the direction of current flow through the coil. The membrane is thereby surrounded with a magnetic field having a field direction opposite to that of the magnetic field of the coil. As a consequence of the resulting repulsion forces, the membrane is rapidly moved away from the coil. A pressure pulse is thereby created in the acoustic propagation medium, which gradually steepens along its propagation path in the medium to form a shockwave. For simplicity, the phenomena which arises in the propagation medium will be always referred to herein as a shockwave, regardless of whether the pressure pulse has steepened to actually form a true shockwave.
A valid approximation for such shockwave generators is that the obtainable peak pressure of the shockwaves increases with the square of the current flowing through the coil. In practice, the coil in conventional shockwave generators must be charged with high-voltage pulses on the order of magnitude of 10 through 20 kV in order to elicit currents in the coil having a magnitude sufficient for generating shockwaves having the required peak pressure, after suitable focusing, for the fragmentation of calculi in the body of a patient. The necessity of having to charge the coil with voltages of this magnitude is considered highly disadvantageous in practice, because the insulating measures required for achieving an adequate electrical strength of the shockwave generator are problematical and extremely complex. Moreover, the high voltages have a disadvantageous effect not only on the surface life of the shockwave generator, but also on the electrical and electromechanical components of the high-voltage generator which is provided for driving the shockwave generator.